Up to this time, there have variously been investigated the characteristic properties of and methods for preparing chitosan derived from the crustaceans such as crabs and shrimps or lobsters (hereunder simply referred to as “crab chitosan”), but there has scarcely been investigated the chitosan originated from plants represented by fungi or mushrooms and methods for the preparation thereof and accordingly, there has scarcely been proposed any article concerning the same.
There have been proposed some research reports on chitosans produced by fungi such as bread mold (Aspergillus niger), Saprolegnia (Achlya) and Actinomycetes. However, it would be quite difficult to cultivate these fungi and there would be a strong probability that the cultivation product thereof may contain unknown toxic substances. Accordingly, the chitosan produced by the fungi could not be used in the applications in which the chitosan should satisfy the strict requirement for the safety to the human body.
On the other hand, it has been known that a trace amount of glucosaimine as a principal constituent of chitosan is included in the hydrophilic solvent extract (commercially sold under the trade name of “Champignon Extract”) from a mushroom (Agaricus bisporus) which has been known to be effective in the treatment of nephropathy, but it has not yet been elucidated whether the trace glucosamine shows any physiological importance or not. Moreover, it has scarcely been tried to positively produce chitosan-containing polysaccharides starting from fungi including the mushroom (Agaricus bisporus).
In Asian district including Japan, fungi such as Lentinus edodes, Auiricularia auriculal, Volvariella Speg (Volvariella volvacea), Lyophyllum Karst (Lyophyllum simeji) and Grifola frondosa have long been used as excellent health foods extensively and widely and they have been considered to be food materials as the basis for ISHOKUDOGEN (both medicines and foods should be based on the same origin). In Europe, mushroom (champignon) (Agaricus bisporus) has widely been used as a food since the 17th century.
The term so-called “mushroom” or “champignon”, in itself, generically means all kinds of fungi, but the term, in a narrow sense, means Agaricus bisporus cultivated in caverns in the suburbs of Paris since the 17th century. In this specification, however, to avoid the occurrence of any misunderstanding, mushroom or champignon is referred to as “Agaricus bisporus”, while the term “fungs (or fungi)” is used for expressing the all kinds of edible mushrooms or champignon.
The annual output of the Agaricus bisporus in the world-wide scale amounts to 2,400,000 to 3,200,000 tons and this corresponds to 30 to 38% of the total output of the fungi cultivated in the whole world and the rate of the Agaricus bisporus cultivated in the united states is 90% of the total output of the fungi cultivated therein. From a historical standpoint, the chitin derived from plants was, for the first time, extracted from mushroom, as a high molecular weight substance insoluble in an alkali medium by Braconnot as a French botanist in 1811. In 1859, Rouget found that the chitin could be converted into a product soluble in an organic acid (solution) when it was heated in a concentrated potassium hydroxide solution and this substance is named as “chitosan” by Hoppe-Seyler in 1894.
A chitin-glucan compound was isolated from Aspergillus niger by Russian research workers during the term extending from 1999 to 2000. It was found that this chitin-glucan compound had a glucan content ranging from 15 to 20%. In this compound, the chitin and glucan are strongly linked to one another through a covalent bond and therefore, they can completely be hydrolyzed only through the treatment with an enzyme (see Non-patent Document Nos. 1 and 2 given below).
In 1981, Shida et al. reported the presence of a skeletal glucan, in Lentinus edodes, insoluble in an alkali medium (24%, at 5° C.). As a result of methylation analysis, it was found that the glucan moiety thereof had a structure consisting of sugar chains having highly branched β-1,6- and β-1,3-bonds. These glucans are bonded to chitin to thus form the internal skeleton of the Lentinus edodes (see Non-patent Document No. 3).
In 1994, Hartland et al. found that an alkali-soluble (1-3) β-glucan was converted into an alkali-insoluble (1-3) β-glucan through the formation of a linkage with chitin on the cell wall of Saccharomyces cerevisiae (see Non-patent Document No. 4).
It has been said that the constituents of the cell walls of fungi and mold are α(1-3) glucan and chitin, but polysaccharides are frequently reconstituted and or reorganized in these fungi during the process of the growth thereof. It has also been believed that the rates of the α- and β-structures vary during the growth cycle of Agaricus bisporus. More specifically, it has been recognized that the rate of β(1-4) increases during the proliferation process, while the rate of β(1-6) increases in the fruiting body thereof.
Even at present, however, the skeletal components of the fungi including chitin have not yet effectively been used, because of their high chemical stability and insolubility in water, dilute acid or alkali solutions or an organic solvent. One of the reasons therefor is that the chitin included in the fungi is insoluble in almost all of the solvents, that it is physiologically inactive, and that it has not been expected to have any usefulness as an ingredient for health foods and drugs.
Among the sugars originated from fungi, β-glucan as a water-soluble component of Lentinus edodes extracted with hot water was found to have immuno-enhancement effect and it has been investigated for use as an adjuvant. In addition, Agaricus bisporus has not chemically been investigated till quite recently, Ricom Corporation has, for the first time, proved that the extract thereof with hot water shows a deodorizing effect and the extract has now been put on the market as a deodorant.
As for most of the other fungi, some of them have been used in health foods as such, quite simply in the form of extracts with hot water or freeze-dried products, In this connection, examples of such other fungi include Coriolus versicolor, Ganoderma lucidum (REISHI) and Agaricus bisporus of Brazil growth.                Non-Patent Documet No. 1: Gamayurova et al., Synthesis of soluble derivatives of chitin-glucan complex. Chemistry and Computational Simulation. Butlerov Communicatios, 1999; No. 1.        Non-Patent Document No. 2: Shabrukova et al., Study of the nature of chitin-glucan complex. Chemistry and Computational Simulation. Butlerov Communicatios, 2001; No. 4.        Non-Patent Document No. 3: Shida et al., Structure of the alkali-insoluble skeletal glucan of Lentinus edodes. J-Biochem-Tokyo, 1981, 90(4):1093–1100.        Non-Patent Document No. 4: Hartland et al., The linkage of (1-3)-β-glucan to chitin during cell wall assembly in Saccharomyces cerevisiae. Yeast, 1994, 10(12):1591-1599.        